An EL element couples a hole and an electron, injected from counter electrodes, in a light emitting layer, excites the fluorescent substance in the light emitting layer by the energy, and emits a light of the color corresponding to the fluorescent substance, attracts the attention as a self light emitting flat display element. In particular, an organic thin film EL display using an organic substance as a light emitting material has a high light emitting efficiency and capable of realizing a high luminance light emission even with less than 10 V applied voltage, capable of emitting a light in a simple element structure, and thus application thereof to the advertisement of displaying a specific pattern by light emission and other inexpensive simple displays is expected.
In the manufacturing of the display using such EL element, in general, an electrode layer and an organic EL layer are patterned. As methods for patterning the EL element, a method of deposition of the light emitting material via a shadow mask, a method of divisional coating by ink jetting, a method of destroying a specific light emitting dye by the ultraviolet ray irradiation, a screen printing method, or the like can be presented. However, in these methods, it was impossible to provide a method for manufacturing an EL element, capable of realizing all of, a high light emitting efficiency, a high light taking out efficiency, a simple manufacturing process, and a high precision pattern formation.
As means for solving these problems, a method for manufacturing an EL element of forming a light emitting layer by patterning using a photolithography method has been proposed. According to the method, compared with the conventionally conducted patterning method by the deposition, since a vacuum equipment comprising a highly accurate alignment mechanism, or the like is not needed, manufacturing can be conducted relatively easily and inexpensively. In contrast, compared with the patterning method using the ink jet method, it is preferable in that a pre-process to a structure, base substance, or the like for aiding patterning, is not conducted. Furthermore, from the relationship with the ejection accuracy of an ink jet head, the photolithography method is considered as a more preferable method for a high precision pattern formation, and thus it is advantageous.
As a method for forming a plurality of light emitting parts by such photolithography method, for example, a method shown in FIG. 5 has been proposed.
First, as shown in FIG. 5A, a patterned first electrode layer 32 is formed on a base substance 31, and furthermore, a first light emitting layer coating solution 33 is coated on the entire surface thereon. Then, as shown in FIG. 5B, a positive type resist 34 is coated on the entire surface, and as shown in FIG. 5C, masking only the part, which a first light emitting part is to be formed, with a photomask 35, it is exposed with an ultraviolet ray 36 excluding the part.
By developing the same with a resist developing agent and cleaning with water, the resist in the exposed part is removed a shown in FIG. 5D. Furthermore, by developing with a solvent of the light emitting layer, as shown in FIG. 5E, the bared first light emitting layer 33 is removed, so that the resist and a first light emitting part 33′ covered with the resist remain.
Then, by the same method for forming the first light emitting part 33′, as shown in FIG. 5F, a second light emitting layer coating solution 37 is coated on the entire surface. At the time, as it is apparent from FIG. 5F, there is a part where the second light emitting layer coating solution 37 coated on the entire surface and the first light emitting part 33′ are contacted with each other. That is, as mentioned above, the first light emitting part 33′ remaining on the base substance 31 has its surface covered with the positive type resist, but the end part “a” developed with the light emitting layer developing agent is bared. Therefore, when the second light emitting layer coating solution 37 is coated thereon, the first light emitting part 33′ and the second light emitting layer coating solution are contacted at the end part “a”. At the time, there is a problem of generating troubles of color mixture or pixel narrowing due to elution of the first light emitting part into the second light emitting layer coating solution.
Furthermore, as shown in FIG. 5G, the positive type resist 34 is coated on the entire surface, and as shown in FIG. 5H, masking the parts, which the first and second light emitting parts are to be formed, with the photomask 35, the other part is exposed with the ultraviolet ray 36.
By developing the same with a resist developing agent, cleaning with water, and furthermore, developing with a solvent of the light emitting layer, as shown in FIG. 5I, only the bared second light emitting layer 37 is removed so that a second light emitting part 37′ covered with the resist 34 is formed.
Furthermore, by the same method for forming the first and second light emitting parts, as shown in FIG. 5J, a third light emitting layer coating solution 38 is coated. At the time, as it is apparent from FIG. 5J, the first light emitting part and the third light emitting layer coating solution are contacted at the end part “a” of the first light emitting part 33′ formed initially, and furthermore, the second light emitting part and the third light emitting layer coating solution are contacted at the end part “b” of the second light emitting part 37′. Similarly, at the time, there is a possibility of generating troubles of color mixture, pixel narrowing, or the like due to elution of the first light emitting part 33′ and the second light emitting part 37′ into the third light emitting layer coating solution.
Furthermore, as shown in FIG. 5K, the positive type resist 34 is coated on the entire surface, and masking the parts, which the first, second and third light emitting parts are to be formed, with the photomask 35, the other part is exposed with the ultraviolet ray 36.
By developing the same with a resist developing agent, cleaning with water, and developing with a solvent of the light emitting layer, as shown in FIG. 5L, only the bared third light emitting layer 38 is removed so that only the part covered with the resist remains. Furthermore, by conducting a peeling treatment with a resist peeling solution, the layers above the part which the resist is formed are peeled off so that the light emitting parts of three colors including the first light emitting part 33′, the second light emitting part 37′ and the third light emitting part 38′ are formed in a bared state as shown in FIG. 5M.
Finally, as shown in FIG. 5N, by forming a second electrode layer 39 on these light emitting parts, an EL element which discharges an EL light emission 40 to the lower direction in the figure can be manufactured.
As mentioned above, according to the photolithography method, since the patterned end part “a” of the first light emitting part and the end part “b” of the second light emitting part are not covered with the photoresist layer, there is a problem that the patterned light emitting parts elute into the light emitting layer coating solution to be coated later at the end part thereof so as to generate color mixture and pixel narrowing at the time of coating the subsequent light emitting layer coating solution.